Flexible Adult Stem Cells, Right There In Your Eye

Promise for future treatments of macular degeneration

January 6, 2012
Source: Cell Press

Finding: Researchers have discovered that there are adult stem cells lying dormant in the RPE cell layer of the retina. The RPE are the retinal cells that normally die first in advanced age-related macular degeneration, accelerating vision loss.

Significance: The new adult stem cells have been found in the eyes of deceased donors with ages ranging from 22 to 99 years old, so everyone probably has them sitting in their retinas from birth. This groundbreaking discovery suggests that a future treatment for macular degeneration could involve stimulating the dormant stem cells to replace damaged retina cells and rescue vision. However, before this can happen the researchers need to further understand how these adult stem cells work and how they could contribute to retinal regeneration.

On behalf of our donors, Macular Degeneration Research—a program of the BrightFocus Foundation—salutes former grantee Dr. Sally Temple and her collaborators for this important work. First author Dr. Enrique Salero was a postdoctoral fellow on Dr. Temple's MDR grant. BrightFocus has been acknowledged as a supporter of the research presented in this publication.

In the future, patients in need of perfectly matched neural stem cells may not need to look any further than their own eyes. Researchers reporting in the January issue of Cell Stem Cell, a Cell Press publication, have identified adult stem cells of the central nervous system in a single layer of cells at the back of the eye.

That cell layer, known as the retinal pigment epithelium (RPE), underlies and supports photoreceptors in the light-sensitive retina. Without it, photoreceptors and vision are lost. The new study shows that the RPE also harbors self-renewing stem cells that can wake up to produce actively growing cultures when placed under the right conditions. They can also be coaxed into forming other cell types.

"You can get these cells from a 99-year-old," said Sally Temple of the Neural Stem Cell Institute in Rensselaer, New York. "These cells are laid down in the embryo and can remain dormant for 100 years. Yet you can pull them out and put them in culture and they begin dividing. It is kind of mind boggling."

Temple's group got the RPE-derived stem cells they describe from the eyes of donors in the hours immediately after their deaths. But the cells can also be isolated from the fluid that surrounds the retina at the back of the eye, which means they are accessible in living people as well.

"You can literally go in and poke a needle in the eye and get these cells from the subretinal space," she says. "It sounds awful, but retinal surgeons do it every day." By comparison, access to most other neural stem cell populations would require major surgery.

Temple said they were curious about the proliferative potential of the RPE given that the tissue is known to be capable of regenerating entire retinas in salamanders. But that plasticity in adulthood had seemed to be lost in mice and chicks. Still, "given the evolutionary evidence, we thought it was worth revisiting," she said.

They placed RPE tissue taken from 22-year-old to 99-year-old cadavers into many culture conditions to see what they could make the cells do. They found one set of conditions that got the cells dividing. Not all of the RPE cells have this regenerative potential, but perhaps 10 percent of them do.

Further work showed that the cells are multipotent, which means that they can form different cell types, though the researchers admit there is more to do to fully explore the cells' differentiation capacity.

There are other implications as well. For example, these cells may explain diseases in which other tissue types show up in the eye. Their presence also suggests that there might be some way to stimulate controlled repair of the eye in the millions of people who suffer from age-related macular degeneration.

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